Speed control device for single phase motors

ABSTRACT

A speed control device for single phase motors is disclosed, which comprises a thyristor connected in series with a motor, and a trigger signal generator means for controlling the triggering phase of the thyristor, said trigger signal generator means including a series circuit of a variable resistor means, a resistor and a rectifier connected between both terminals of an a-c source and a capacitor connected between the cathode of said thyristor and the connection of said variable resistance means and said resistor and also across the cathode and the anode of said thyristor. The variable resistor means includes a light source, a light-sensitive element facing the light source and having its resistance varied in accordance with the amount of incident light from the light source, and a movable shutter plate interposed between the light source and the light-sensitive element and capable of being moved between a position to interrupt the light from the light source and a position not to interrupt the light from the light source.

United States Patent 1 Soeda May 29, 1973 [541 SPEED CONTROL DEVICE FOR 3,493,832 2 1970 Kay ..3l8/331 x SINGLE PHASE MOTORS 3,508,134 4/1970 Dosch et al t ..318/33l 3,582,738 6/1971 Claassen ..318/33l X [75] Inventor: KatSlIjI Soeda, Sukagawa-sh1, Japan [73] Assignee: Yamamoto Electric Industrial Co., Primary z-kubinson Ltd., Sukagawa-shi, Ja an Attorney-James E. Armstrong and Harold C. Wegner [22] Filed: Oct. 12, 1971 21 Appl. No.: 188,273 ABSTRACT Related Application Dan A speed control device for single phase motors is disclosed, WhlCl'l comprises a thyristor connected 1n se- [63] Continuation-impart of Ser. No. 139,567, May 3, ries with a motor, and a trigger signal generator means 197], abandoned.

for controlling the triggering phase of the thyristor, said trigger signal generator means including a series [30] Foreign Application Priority Data circuit of a variable resistor means, a resistor and a May 31, 1971 Japan ..46/44923 rectlfier connected between both termmals source and a capacitor connected between the cathode of said thyristor and the connection of said 9? variable resistance means and said resistor and also 58 480 across the cathode and the anode of said thyristor. 1 0 care 318/245 The variable resistor means includes a light source, a

light-sensitive element facing the light source and having its resistance varied in accordance with the [56] References C'ted amount of incident light from the light source, and a UNITED STATES PATENTS movable shutter plate interposed between the light source and the light-sensitive element and capable of 3,582,744 6/1971 Coffey ..318/345 being moved between a position to interrupt the light 3,424,967 H1969 Keller "318/480 from the light source and a position not to interrupt 3,366,862 H1968 Beck ..318/48O the light from the light soul-ca 3,319,591 /1967 Hamlett ..3l8/331 X 6 Claims, 5 Drawing Figures 32 20 1 23 fjfi 2/ 2 9 I X A L i 1 4 a I 2 H95 5 10, 51 v I A m l E8 It. s 9 A 4C PUWU? SOURCE Patented May 29, 1973 I5 Sheets-Sheet 2 Patented May 29, 1973 3 Sheets-Sheet 3 A. C POWER SOURCE STROKE LENGTH OF PEDAL OEPRESS/ON SPEED CONTROL DEVICE FOR SINGLE PHASE MOTORS CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of a copending US. Pat. Application Ser. No. 139,567 filed on May 3, 1971 by the same applicant and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a speed control device for single phase motors and, more particularly, to speed control systems for controlling the speed of series wound motors and universal motors by controlling the triggering phase of a thyristor.

2. Description of the Prior Art Series-wound motors and universal motors have been extensively used as the drive of motor-driven household apparatus such as motor-driven sewing machines. Usually, the speed of these motors is controlled by varying the resistance of a carbon pile or coiled resistor connected between the motor and a power source.

However, this type of motor speed control by varying the source voltage by means of a series resistor inevitably leads to large power losses. Also, the speed control unit itself tends to be relatively large in size.

. SUMMARY OF THE INVENTION An object of this invention is to provide an improved speed control for single phase motors, which is compact in construction and is capable of reducing power losses.

The speed control system for single phase motors according to this invention comprises a thyristor connected in series with a motor, and a trigger signal generator for controlling the triggering phase of the thyristor, said trigger signal generator including a variable resistor means connected to an a-c source and adapted to provide a controlled voltage waveform and a series circuit having a rectifier and a capacitor, said thyristor being triggered in accordance with said controlled voltage waveform prevailing at its gate electrode.

In accordance with this invention, the afore-said variable resistor means is constituted by a light source, a light-sensitive element having its resistance varied in accordance with the quantity of incident light from said light source and a movable shutter plate intervening between said light source and movable between a position to interrupt the light from said light source and a position not to interrupt the light from said light source.

According to this invention, there is no need to connect a variable resistive means between the motor and a power source, so that the size of the speed control unit and the power loss may be reduced compared to the prior art speed control unit for single phase motors.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an embodiment of the speed control unit for single phase motors according to this invention.

FIG. 2 is an exploded perspective view of an example of the variable resistor means.

FIG. 3 is a side view, partly in section, showing the speed control unit according to this invention.

FIG. 4 is a circuit diagram of another embodiment of the speed control unit for single phase motors according to this invention.

FIG. 5 shows relation between the stroke length of pedal depression and the number of motor revolution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a preferred embodiment of the speed control according to this invention. Reference numeral 1 designates a series-wound motor or universal motor as the sewing machine drive. On the sewing machine proper, there are provided a power source switch 10 and a pilot lamp 11. The leads of these parts are taken to a connector 13. The main parts of the control unit are assembled in a casing as shcematically indicated by a dashed rectangle 20. Leads from the speed control unit and leads from a connection plug 9 for connection to a power source are taken to a connector 12. For the operation of the sewing machine, for instance, the connectors l2 and 13 are connected together and the connection plug 9 is inserted into a receptacle leading to a power source. The connector 12 has terminals 3 and 4 connected to the connection plug 9. A circuit leading from the terminal 3 through a terminal 6 of the connector 13, the power source switch 10, a terminal 8 of the connector 13, the motor 1, a terminal 5 of the connector 13, a terminal 2 of the connector 12, a thyristor 22, and a noise elimination coil 39 to the terminal 4 constitutes a power circuit for the motor 1. Between the terminals 3 and 4 is connected a series circuit of a resistor 23, a light-sensitive element (CdS) 24, a variable resistor 29, a resistor 30 and a diode 31. The connection point 40 between variable resistor 29 and resistor 30 is connected through a diode 32, a capacitor 33 and the connector terminals 2 and 5 to one side of the motor 1. The capacitor 33 is connected between the cathode and gate of the thyristor 22. It is also connected in parallel with a circuit of a thermistor 35 and resistors 34 and 36. A variable resistor 28 is connected in parallel with the CdS 24.

The CdS 24, a fluorescent lamp 26 connected between the terminals 3 and 4 of the connector 12 and a movable shutter plate 25 are assembled together to constitute a variable resistive means as is enclosed within a dashed rectangle 21.

FIG. 2 shows the variable resistive means in detail. The CdS 24 and fluorescent lamp 26 are mounted in respective mounts 54 and 53 such that they face each other. interposed between these mounts 54 and 53 is the movable shutter plate 25 which is secured to an arm member 55 rotatable about a pin 52. When the arm 55 is rotated by a spring 51 in the clockwise direction, a movable shutter plate 25 is moved to a position not to interrupt the light flux from the fluorescent lamp 26 directed toward the CdS 24. With the clockwise rotation of the arm member 55, the movable shutter plate 25 comes to assume a position to interrupt the light directed from the lamp toward the CdS. The internal resistance of the CdS being varied by varying the quantity 7 of light incident on the CdS.

In the operation of the motor speed control unit of the above construction, when the power source switch 10 is closed after connecting the connectors 12 and 13 and inserting the connection plug 9 into a power source receptacle, the pilot lamp 11 is turned on, indicating that the power source voltage prevails.

At the same time, current is caused to pass through the resistor 23, CdS 24, variable resistor 29, resistor 30 and diode 31, so that a predetermined voltage appears on the connection point 40. Since the motor 1 remains still at this time, the voltage drop across it is zero and the terminals 2 and 3 are at the same potential. Thus, during the half source cycle during which the potential of the terminal 4 is positive, the potential on the connection point 40 is higher than that of the terminal 2, so that the capacitor 33 is charged. The voltage developed across the capacitor 33 has a phase and an amplitude determined by the capacitance of the capacitor 33 and the resistance values of the resistors 23, 29, 30 and the CdS 24. This voltage is applied to the gate of the thyristor 22.

Meanwhile, the movable shutter plate 25 normally assumes a position to interrupt the light flux from the fluorescent lamp 26, so that the C118 24 normally offers a maximum resistance. Under this condition, the potential on the connection point 40 is too low todevelop a sufficient voltage across the capacitor 33 to trigger the thyristor 22. This is so arranged by appropriately selecting the resistance of the resistor 23, variable resistors 28 and 29 and resistor 30.

With the movement of the movable shutter plate 25 as the arm member is rotated by the spring force in the clockwise direction in FIG. 2, the quantity of light incident on the CdS 24 progressively increases to decrease the resistance thereof, thus increasing the potential on the connection point 40 to increase the voltage across the capacitor 33 and simultaneously to lead the phase thereof. Consequently, when the anode of the thyristor 22 is applied with a positive half cycle of the source voltage and simultaneously the movable shutter plate 25 is rotated to a point where the voltage across the capacitor 33, i.e. the voltage applied to the gate of the thyristor 22, has a value sufficient to trigger the thyristor 22, the thyristor 22 is triggered to start the motor 1. When the motor is started, a voltage proportional to the motor speed is induced to change the potential of the terminal 2. With the changing potential of the terminal 2 the waveform of the terminal voltage across the capacitor 33 changes accordingly, thus changing the triggering phase of the thyristor 22. The waveform of the voltage across the capacitor 33 depends upon the relation between the potential on the connection point 40 and the potential on the terminal 2 which depends upon the motor speed, while the motor current, which determines the motor speed, depends upon the trigger angle of the thyristor 22, which in turn depends upon the voltage across the capacitor 33. Accordingly, the motor speed is dependent upon the potential at the point 40. When the movable shutter plate 25 is further revolved in the clockwise direction, the potential on the connection point 40 is raised to increase the motor speed upto a value where the above relation is satisfied.

In the embodiment of FIG. 1, a constant voltage discharge tube 37 such as a neon lamp is provided. By virtue of this tube the peak value of the potential on the connection point 40 is constant irrespective of fluctuations of the source voltage, so that a reliable motor speed control can be ensured. The variable resistor 28 connected in parallel with the CdS 24 may be appropriately adjusted such that the motor 1 is started when the movable shutter plate 25 comes to a desired position. The variable resistor 29 is provided for adjusting the maximum motor speed. 1

As described earlier, in a half cycle of the source voltage during which the potential of the terminal 4 is positive the thyristor 22 is triggered to cause the motor current to flow. During the subsequent half cycle during which the potential of the terminal 4 is negative, the thyristor 22 is of course off, and during this time the charge on the capacitor 33 is discharged through the discharging circuits of resistors 34, 35 and 36.

The thermistor 35 is closely fixed to the thyristor 22, so that a temperature rise of the thyristor 22 causes a similar temperature change of the thermistor 35. Thus, when the trigger characteristic of the thyristor 22 changes due to a temperature rise thereof, it is compensated for by the corresponding change of the resistance of the thermistor 35. With an increase in the temperature of the thermistor 35, its resistance decreases to decrease the potential on the connection point 40, thus decreasing the voltage developed across the capacitor 33, since the charging current into the capacitor 33 depends upon the difference between the potential on the connection point 40 and the potential on the terminal 2. In this manner, change of the operating point of the thyristor 22 due to a temperature rise thereof can be compensated for.

FIG. 4 shows a circuit diagram of another embodiment according to the present invention. In the embodiment as shown in FIG. 1, the trigger signal of the thyristor 22 is affected by the induced voltage of the motor 1 and hence, the control characteristics of the circuit are excellent in a relatively low speed range, but not so in a high speed range. The circuit in FIG. 4 is aimed at improvement of the control characteristics in the high speed range. In FIG. 4, a switch means is provided so that the cathode of the diode 31 is selectively connected through a contact 71 to a contact 72 which is connected to the terminal 2 or to a contact 73 which is taken directly to the cathode of the thyristor 22. When the contacts 71 and 72 are closed and the contacts 71 and 73 are opened, the circuit is entirely the same as that in FIG. 1. When the contacts 71 and 72 are opened and the contacts 71 and 73 are closed, the cathode of the thyristor 22 is connected to the gate thereof through the diode 31, the resistor 30 and the diode 32. Thus, the motor circuit is not included in the gate circuit of the thyristor 22 and consequently, the trigger signal of the thyristor 22 is not affected by the induced voltage of the motor 1, but only dependent on the resistance value of the CdS 24, which results in improvement of the control characteristic in a high speed range. FIG. 5 shows the relation between the number of motor revolutions and the stroke length of pedal depression which determins the resistance value of the CdS 24. When the contacts 71 and 72 are closed, the

pivotally attached to the casing 57 by a pin 58 so as to,

be adaptable to serve as a pedal. The afore-mentioned variable resistive means 21 is secured to the casing 57. The arm member 55 carrying the movable shutter plate 25 is urged by the spring 51 in the clockwise direction.

its free end is urged against the inner surface of the cover 56, and it is usually held in a position as indicated by solid lines by force of a spring 61. In this position of the arm member 55, the movable shutter plate 25 completely shuts the light flux from the light source 26 and no light flux is incident on the CdS 24. When a portion 59 of the cover is depressed, the cover is rotated in a clockwise direction. As a result, the arm member 55 is rotated by the spring force of the spring 51 in a clockwise direction. With the rotation of the arm member 55, the movable shutter plate 25 progressively departs from the path of the light flux from the light source 26. Thus, the motor speed may be controlled by appropriately depressing the pedal cover 56.

I claim:

1. A speed control device for controlling the speed of a universal motor comprising a thyristor connected in series with a universal motor to an AC power source and trigger signal generating means for supplying the gate of said thyristor with a controlled trigger signal, said trigger signal generating means comprising a capacitor connected at one end to the cathode of said thyristor and at the other end to a gate, a series circuit of a variable resistance means, a resistor and a rectifier, a constant voltage discharge element connected in parallel to said series circuit, first circuit means for connecting said other end of said capacitor to the junction of said variable resistance means and said resistor, and second circuit means for connecting said series circuit to said AC power source, said variable resistance means comprising a light source, a light-sensitive resistance element having a resistance value variable responsive to light rays of said light source and a movable shutter adaptable to continuously change the amount of light rays incident to said light-sensitive element.

2. A speed control device according to claim 1, wherein said second circuit means comprises switch means selectively changeable between a first position where said series circuit is connected directly between said both terminals of said AC power source and a second position where said series circuit is connected through said motor between said both terminals.

3. A speed control device according to claim 1, further comprising a temperature-sensitive resistance means thermally coupled to said thyristor and connected in parallel with said capacitor.

4. A speed control device according to claim 1, wherein said movable shutter of said variable resistance means is urged in one direction of the movement of the same by a spring means.

5. A speed control device according to claim 3, wherein said thyristor and said trigger signal generator means are accommodated in a casing provided with a cover pivoted to said casing, the movement of said movable shutter being interlocked to the pivotal motion of said cover.

6. A speed control unit to be used for controlling the speed of a universal motor comprising a speed control device which comprises a thyristor connected in series with a universal motor to an AC power source and trigger signal generating means for supplying the gate of said thyristor with a controlled trigger signal, said trigger signal generating means comprising a capacitor connected at one end to the cathode of said thyristor and at the other end to the gate, a series circuit of a variable resistance means, a resistor and a rectifier, a constant voltage discharge element connected in parallel to said series circuit, first circuit means for connecting said other end of said capacitor to the junction of said variable resistance means and said resistor, and second circuit means for connecting said series circuit to said AC power source, said variable resistance means comprising a light source, a light-sensitive resistance element having a resistance value variable responsive to light rays of said light source and a movable shutter adaptable to continuously change the amount of light rays incident to said light-sensitive element; a casing having an open space for mounting therein said control device, a cover mounted on said casing so as to enclose said open space and to be pivotally movable in a pedal action, spring means for biasing said cover in one direction of said pedal action, means for movably mounting said movable shutter in said casing, and means for mechanically transmitting the movement of said cover to said movable shutter thereby causing said movable shutter to move with said pedal action. 

1. A speed control device for controlling the speed of a universal motor comprising a thyristor connected in series with a universal motor to an AC power source and trigger signal generating means for supplying the gate of said thyristor with a controlled trigger signal, said trigger signal generating means comprising a capacitor connected at one end to the cathode of said thyristor and at the other end to the gate, a series circuit of a variable resistance means, a resistor and a rectifier, a constant voltage discharge element connected in parallel to said series circuit, first circuit means for connecting said other end of said capacitor to the junction of said variable resistance means and said resistor, and second circuit means for connecting said series circuit to said AC power source, said variable resistance means comprising a light source, a light-sensitive resistance element having a resistance value variable responsive to light rays of said light source and a movable shutter adaptable to continuously change the amount of light rays incident to said light-sensitive element.
 2. A speed control device according to claim 1, wherein said second circuit means comprises switch means selectively changeable between a first position where said series circuit is connected directly between said both terminals of said AC power source and a second position where said series circuit is connected through said motor between said both terminals.
 3. A speed control device according to claim 1, further comprising a temperature-sensitive resistance means thermally coupled to said thyristor and connected in parallel with said capacitor.
 4. A speed control device according to claim 1, wherein said movable shutter of said variable resistance means is urged in one direction of the movement of the same by a spring means.
 5. A speed control device according to claim 3, wherein said thyristor and said trigger signal generator means are accommodated in a casing provided with a cover pivoted to said casing, the movement of said movable shutter being interlocked to the pivotal motion of said cover.
 6. A speed control unit to be used for controlling the speed of a universal motor comprising a speed control device which comprises a thyristor connected in series with a universal motor to an AC power source and trigger signal generating means for supplying the gate of said thyristor with a controlled trigger signal, said trigger signal generating means comprising a capacitor connected at one end to the cathode of said thyristor and at the other end to the gate, a series circuit of a variable resistance means, a resistor and a rectifier, a constant voltage discharge element connected in parallel to said series circuit, first circuit means for connecting said other end of said capacitor to the junction of said variable resistance means and said resistor, and second circuit means for connecting said series circuit to said AC power source, said variable resistance means comprising a light source, a light-sensitive resistance element having a resistance value variable responsive to light rays of said light source and a movable shutter adaptable to continuously change the amount of light rays incident to said light-sensitive element; a casing having an open space for mounting therein said control device, a cover mounted on said casing so as to enclose said open space and to be pivotally movable in a pedal action, spring means for biasing said cover in one direction of said pedal action, means for movably mounting said movable shutter in said casing, and means for mechanically transmitting the movement of said cover to said movable shutter thereby causing said movable shutter to move with said pedal action. 